He studied and published the first analysis of a complete Neanderthal specimen. The fossil discovered in La Chapelle-aux-Saints was an old man, and Boule characterized it as brutish, bent kneed and not a fully erect biped.[1] In an illustration he commissioned, the Neanderthal was characterized as a hairy gorilla-like figure with opposable toes, according to a skeleton which was already distorted with arthritis. As a result, Neanderthals were viewed in subsequent decades as being highly primitive creatures with no direct relation to anatomically modern humans. Later re-evaluations of the La Chapelle-aux-Saints skeleton have roundly discredited Boule's initial work on the specimen.[2]

Boule also expressed some scepticism about the "Piltdown man" discovery—later revealed to be a hoax. As early as 1915, Boule recognized that the jaw belonged to an ape rather than an ancient human.[4] However, the Piltdown forgery has been characterised as providing evidential support for Boule's "branching evolution" conclusions drawn from his Neanderthal research—research which is likewise said to have "prepar[ed] the international community for the appearance of a non-Neanderthal fossil such as Piltdown Man."[2]